FIG. 1 shows a schematic diagram illustrating the structure of a general color cathode ray tube. As shown in FIG. 1, the color cathode ray tube generally includes a glass envelope having a shape of bulb and being comprised of a faceplate panel 1, a tubular neck 13, and a funnel 2 connecting the panel 1 and the neck 13.
The panel 1 comprises faceplate portion and peripheral sidewall portion sealed to the funnel 2. A phosphor screen 4 is formed on the inner surface of the faceplate portion. The phosphor screen 4 is coated by phosphor materials of R, G, and B. A multi-apertured color selection electrode, i.e., shadow mask 3 is mounted to the screen with a predetermined space. The shadow mask 3 is hold by main and sub frames 7 and 8. An electron gun is mounted within the neck 13 to generate and direct electron beams 6 along paths through the mask to the screen.
The shadow mask 3 and the frame 7 constitute a mask-frame assembly. The mask-frame assembly is joined to the panel 1 by means of springs 9.
The cathode ray tube further comprises an inner shield 10 for shielding the tube from external geomagnetism and a reinforcing band 12 attached to the sidewall portion of the panel 10 to prevent the cathode ray tube from being exploded by external shock. The cathode ray tube further comprises external deflection yokes 5 located in the vicinity of the funnel-to-neck junction and a magnet 11 attached to the rear side of the deflection yokes 5 for amending electron bean trajectory.
Process for making the color cathode ray tube comprises generally pre-process and post-process.
During the pre-process, phosphor materials are deposited on the inner surface of the panel.
The post-process comprises further sub processes as follows. Firstly, after the phosphor materials are deposited, sealing process is performed. In the sealing process, a panel to which mask-frame assembly is mounted and a funnel on the inner surface of which frit is deposited is sealed together in a high temperature furnace. Then, evacuating process is performed where electron gun is inserted in the neck. Thereafter, an evacuating and sealing process is performed, in which the cathode ray tube is evacuated and sealed.
Since the cathode ray tube is evacuated, it suffers from high tensile and compressive stress. Therefore, a reinforcing process is conducted where reinforcing band 12 is attached to the panel to distribute the stress over the panel.
FIG. 2 shows a schematic view of distributions of stresses generated in the panel and funnel glasses after the evacuation process. In FIG. 2, dotted and solid lines represent compressive and tensile stresses, respectively.
In general, when a glass gets a shock from outside, cracks appear in the glass. Tensile stress may hasten increase of the cracks such that the glass may even be broken by the cracks. On the contrary, compressive stress disturbs increase of the cracks. As shown in FIG. 2, central portion of the panel gets compressive stress while corner portion and seal line portion get tensile stress. Therefore, the central portion is relatively strong against shock. However, the corner portion and the seal line portion are easily broken by outside shock.
Moreover, the cathode ray tube becomes slim recently. As the cathode ray tube becomes slimmer, stress problem becomes more severe. This is because volume of the panel decreases while the degree of vacuum is not changed as the cathode ray tube becomes slimmer.
Further, the cathode ray tube where the funnel portion where yokes are attached are made to have rectangular shape to reduce power consumption suffers larger tensile stress. Those cathode ray tubes are easily broken during heat treatment processes.
In order to reduce the effect of the tensile stress on the funnel glass, heat treatment is conducted for the cathode ray tube to generate compressive stress for increasing shock tolerance. However, those treatments increase manufacturing costs.